The invention relates to the area of making chemical products from renewable materials. Specifically, the invention relates to compositions, methods, and apparati for improving the removal of lignin from its aqueous suspensions. As described, for example, in U.S. Pat. No. 8,030,039, lignocellulosic materials (i.e. plant matter) can be processed to obtain a number of useful items such as cellulose, paper, pulp, plastics, alcohols, organic compounds, combustible fuels, and sugars. To obtain the various end products, however, a number of separation and processing steps must be performed. One of the most crucial steps is the separation of solid dispersed lignin from a liquid phase.
Lignin is a highly complex polyphenolic compound, which is an integral part of the secondary cell walls of plants. It is one of the most abundant organic polymers on Earth and typically constitutes between a quarter and a third of the dry mass of wood. In plants, lignin provides structural support by forming covalent bonds that cross-link with cellulose and hemicellulose in plant xylem cells.
The specific chemical nature of lignin prevents it from depolymerization in common plant biomass processing technologies that involve carbohydrate depolymerization and dissolution. Its subsequent removal as a solid phase then is required because the presence of lignin is known to impair many water based processing steps such as fermentation. Also lignin contains numerous carbonyl and aromatic groups which are highly reactive and interfere with numerous chemical processing steps. As a result, most techniques for processing lignocellulosic materials attempt to remove lignin quite early in the process. For example US Published Patent Application 2007/0259412 describes the production of ethanol biofuel from lignocellulosic materials which involves separating lignin from cellulose and then converting the cellulose into biofuel. Other examples are U.S. Pat. Nos. 296,935 and 8,366,877 which describes methods of removing lignin from wood pulp before producing paper. In addition, lignin is also removed because it has been found to be useful for various purposes for example as a dispersant, a flocculant, a tanning agent, and to be burned as an energy source. Efficient lignin removal is essential for the economic viability of plant biomass processing.
Some examples of biomass processing involving lignin removal are described in U.S. Pat. No. 8,043,839, European Patent Publication EP2336193, and Scientific Papers: Hydrolysis if Lignocellulosic Materials for Ethanol Production: a Review, by Y Sun et al., Bioresource Technology vol. 83, pp. 1-11, (2002), and Pretreatment of Corn Stover by Aqueous Ammonia, by T Kim et al., Bioresource Technology vol. 90, pp. 39-47, (2003) and U.S. Pat. No. 8,043,839. Such methods include hydrolysis, e.g., acid hydrolysis, autohydrolysis, steam explosion, ammonia fiber explosion, ozonolysis, acid hydrolysis, alkaline hydrolysis, oxidative delignification, biological/enzymatic delignification, as well as degrading by other methods of the cellulose or hemicelluloses from the lignin. Unfortunately, because of how deep within the cell wall the lignin resides, as well as lignin's innate stiffness, and tendency to recondensate during delignification, all existing bioprocessing methods have difficulty with fast lignin removal from the aqueous phase due to its finely dispersed nature and difficulty to coagulate and settle down; for the same reason filtering dispersed lignin out is always a cumbersome and lengthy process. This stage makes processing lignocellulosic materials longer and less economically attractive. As a result there is clear utility in novel methods, compositions, and apparati for improved removal of lignin from process solutions in technologies involving lignocellulosic materials.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.